The present invention generally relates to an image forming apparatus employing a media sheet coated with photo-setting microcapsules and more particularly, to a method of loading the media sheet, in which a front end portion of the newly mounted media sheet of a rolled form is drawn up to a predetermined position.
Japanese Patent Laid-Open Publication No. 58-88739 laid open for public inspection on May 26, 1983 discloses an image forming method which employs a media sheet coated, on its surface, with photo-setting microcapsules (hereinbelow, referred simply to as "microcapsules") containing photo-setting material and colorless dye and an image receiving sheet coated with developing material causing a color development reaction with the colorless dye of the microcapsules. In this known image forming method, after the media sheet has been subjected to exposure by an image of an original document, the media sheet and the image receiving sheet are pressed against each other. The microcapsules are set at a portion of a surface of the media sheet, which portion has received light of exposure of the image of the original document and thus, a selectively set image is formed on the surface of the media sheet. When the media sheet is placed on the image receiving sheet so as to be pressed against the image receiving sheet, the unset microcapsules of the media sheet are ruptured, so that the colorless dye contained in the microcapsules oozes out of the microcapsules. This colorless dye causes a color development reaction with the developing material on the image receiving sheet and thus, an image can be obtained on the image receiving sheet.
The media sheet employed in the known image forming method is wound in a rolled form such that the surface having the microcapsules coated thereon faces inwardly for the purpose of preventing such phenomena that the microcapsules are ruptured by external forces before an image forming operation and that the microcapsules are set by external light. Meanwhile, the media sheet wound in a rolled form is provided as a cartridge such that the media sheet can be easily mounted on a supply portion of an image forming apparatus. The media sheet mounted on the supply portion is introduced by a plurality of rollers into a transport passage having an exposure position and a pressing position. The media sheet having passed through the pressing position is taken up by a take-up shaft.
However, the media sheet has a thickness of as small as about 25 .mu.m and pressure rollers at the pressing position are pressed against each other at a linear pressure of 80-90 kg/cm so as to rupture the microcapsules. Therefore, in the case where a loading operation of the media sheet, in which a front end portion of the media sheet mounted on the supply portion is drawn out of the cartridge and is taken up by the take-up shaft through the transport passage, is performed manually, the loading operation is quite troublesome. Meanwhile, if an error in position for mounting the front end portion of the media sheet on the take-up shaft is produced at the time of the loading operation, such inconveniences are incurred during subsequent use that the media sheet are fed obliquely and wrinkles are produced on the pressure rollers
Thus, the present inventor previously proposed a loading method in which when a door of the image forming apparatus has been closed after the front end portion of the media sheet mounted on the supply portion was drawn up to a predetermined position by the operator, rollers and the pressure rollers at the transport passage are rotated together with the take-up shaft such that the front end portion of the media sheet is automatically taken up by the take-up shaft.
However, in manufacturing processes of the prior art image forming apparatus, there is slight difference in tolerance of parallel between the take-up shaft and the pressure rollers. Therefore, when the media sheet wound in a rolled form is transported continuously for a long term, the above slight difference accumulates so as to produce a large nonuniformity in position of the media sheet in an axial direction of the rollers. As a result, such problems arise that a side edge of the media sheet is brought into contact with a guide and a portion of an image of an original document is not exposed onto the media sheet at the time of exposure of the media sheet, thereby resulting in partial formation of the image of the original document.